Showing 9 results for Trapezoidal
M.h. Omid, M.esmaeeli Varaki,
Volume 9, Issue 2 (7-2005)
Abstract
خTo reduce the construction costs of stilling basins of hydraulic jump type is sometimes, novel geometries are sometimes used to adopt the basin to the upstream and downstream sections without any transition structures. Otherwise, any changes in the geometry of the basin would cause changes in the conditions and characteristics of the hydraulic jump. In this study, the effects of variation in both the side slopes and the diverging angle of a gradually expanding stilling basin with trapezoidal section on the jump condition were experimentally investigated. The experimental tests were conducted in a specially designed model for a wide range of side slopes and longitudinal divergences of the basin walls. The important parameters of the jump, such as the length, sequent depth and the rate of energy loss were computed and compared to those in the normal jumps. Tests were conducted for three different side slopes (0.5:1, 1:1, 1.5:1) and four diverging angle (3o , 5 o, 7o, 9o) with the straight jump in the rectangular section and in the wide scope of decsent numbers (from 3 to 9). The results indicate that any decrease in the side wall slopes for a particular angle of divergence would cause a reduction in the sequent depth and an increase in the jump length and energy loss compared to the rectangular section on the same angle of divergence. It is also found that the longitudinal divergence of the side walls for a particular side slope will increase the stability of the jump within the stilling basin. It will also cause a reduction in the sequent depth and the jump length as well as an increase in energy loss of the jump, when compared to the straight jumps in either rectangular or trapezoidal sections.
M. Karami Moghaddam, M. Shafai Bajestan, H. Sedghi,
Volume 15, Issue 57 (10-2011)
Abstract
In diversion flows, a portion of stream flow which enters the intake is diverted from upstream of the intake denoted by a surface and is called dividing stream surface (DSS). The amount of flow and sediment discharge entering the intake as well as design of submerged vanes to control sediment depends on determination of dividing stream width. In this study, the experimental tests were carried out at a 30 degree water intake from a trapezoidal section. Three components of velocity data were obtained for different flow conditions. Then numerical SSIIM2 model was calibrated and verified using tests data. More flow conditions such as the main channel with rectangular section were run using SSIIM2 model to get enough hydraulic data. From analysis of these datas it was found that the dividing stream width in different distances from the bed depends directly upon the diversion flow ratio. It was found that in comparison to the rectangular section, in trapezoidal cross section, the DSS dimensions are modified in such a way that its width is increases at the surface and reduced at the bed for the same flow conditions. Relations for predicting the dividing stream width and diversion flow ratio have been presented in this paper for intake from both rectangular and trapezoidal cross sections.
M. Heidarpoor, S. H. Razavian, Y. Hosseini,
Volume 18, Issue 68 (9-2014)
Abstract
The combined system of gate and weir is used for flow measurement in open channels. But in case the passing water has floating material and sediment it damages their performance and hence error of measurement will increase. In order to solve this problem, weir and gate can be combined and a concentrated hydraulic system known as weir-gate can be developed, thus allowing sediments transportation from under the gate and floating particles on weir. The principal goal of this study was to investigate the passing flow characteristics by trapezoidal weir and sharp-edge rectangular sluice gate in rectangular channel, and also suggest a discharge coefficient for combinational flow in different flow conditions. The experiments were carried out in laboratory channel on models with different geometric dimensions under various hydraulic conditions. Discharge coefficient was presented for various condition of passing flow of trapezoidal sharp-edge weir and below rectangular sluice gate using statistical analysis conducted on dimensionless geometric parameters affecting the flow. Resulting discharge coefficients were in agreement with laboratory results.
S. M. Seyedian, M. Karami Moghadam, Y. Ramezani,
Volume 21, Issue 4 (2-2018)
Abstract
The study of flow patterns in front of intake has been attracted the attention of researchers during the past decades to explore the mechanism of flow and sediment entry to the intake. In this study, the separation and stream tube dimensions were investigated in water intakes installed to rectangular and trapezoidal main channel. These researches were carried out with experimental and fluent models. The results of experimental and fluent models have a good conformity. It was found that, in trapezoidal main channel, the stream tube width decreases near the bed and increases near the surface and separation dimensions reduced and led to reduction of sediment entry and increase of efficiency
Gh. Safarinejadi, M. Heidarnejad, A. Bordbar, M. H. Pourmohammadi, A. Kamanbedast,
Volume 23, Issue 4 (12-2019)
Abstract
The use of free launch jets in flip bucket structures with associated submerged ponds, in the appropriate geological, and topographic and hydraulic conditions, could have significant economic and safety benefits. In this research, the downstream scour phenomenon of a flip bucket jet was investigated in free conditions, as well as in the presence of a trapezoidal and triangular slot in the coastal manner with different layout intervals at flow rate of 9, with a total of 45 experiments. The results of this study showed that the presence of the slot had significant effects on the depth and range of scour, so that the fit bucket jet with alternate triangular slots reduced the scour by about 12.7%, as compared to the no slot mode. Moreover, the maximum scour depth occurred in the bucket mode with the alternate trapezoidal slots in the more favorable interval than the rest of the models. Then, the results were compared with several empirical formulas and Veronese A relation showed closer results to the actual values.
R. Gharibvand, M. Heidarnejad, H. A. Kashkouli, H. Hasoonizadeh, A. Kmanbedast,
Volume 24, Issue 1 (5-2020)
Abstract
The flow fields over a trapezoidal labyrinth weir (two-cycle) and a piano key weir were simulated using Flow3D, studying the impact of each model on the flow field in the weirs and the coefficient of discharge in comparison with the available experimental data. Moreover, the models were investigated experimentally in a 12.5 m long, 0.3 m wide, and 0.4 m high rectangular flume under clear-water conditions. The results showed good agreement between the data from the numerical and experimental models. The piano key weirs had a higher coefficient of discharged compared with labyrinth weirs. The coefficient of discharge was observed to increase by 26 percent as the height of the PKW was increased by 50 percent (from 5 to 7.5 cm). This increase was 24 percent for labyrinth weirs.
A. Moghtaderi, E. Valizadegan,
Volume 25, Issue 2 (9-2021)
Abstract
In this study, the hydraulic characteristics of the flap gates are installed at the end of the trapezoidal channels were investigated by laboratory study. In the physical model, three trapezoidal channels and four gates with different weights were used (12 gates for three channels). Based on several experiments, equations for estimating of flow rate for each side slope (each channel) were developed using dimensional analysis. In this research, five forms of discharge-stage relationship were used to obtain relationships for each side slop to estimate flow rate, separately. The results show that none of the discharge-stage relationships forms as a single relationship for all flap gates in a certain channel are suitable for estimating discharge. But the first, second, and third forms of the discharge-stage relationship are very suitable for estimating the flow rate in a certain channel for a certain flap gate. In other words, for each gate with a specific weight, a separate (unique) relationship is obtained to estimate the flow rate in the form of the first to the third discharge-stage relationship in a certain channel. To estimate of flow rate by using the first form of the discharge-stage relationship, the maximum values of statistical parameters of RMSE, ME, and MARE, among all three channels, are 0.0001 m3/s, 0.00022 m3/s, and 0.22 percent, respectively. The values of all the above statistical parameters for the first, second, and third forms of the discharge-stage relationship are presented in the article.
J. Meshkavati Toroujeni, A.a. Dehghani, A. ٍemadi, M. Masoudian,
Volume 25, Issue 3 (12-2021)
Abstract
One of the crucial problems that exist in the irrigation networks is the fluctuation of the water surface flow in the main channel and changes in the flow rate of the intake structure. One of the effective methods to decrease these fluctuations is increasing the weir crest length at the given width of the channel with the use of the labyrinth weirs can be achieved for this purpose. The labyrinth weir is the same linear weir that is seen as broken in the plan view. In this study, a labyrinth weir with a length of 3.72 m, three different heights of 15, 17, and 20 cm, three different shapes of dentate (rectangular, triangular, and trapezoidal), and a linear weir were used in a recirculating flume with 15 m length and 1 m width. The result showed that for a given length and height of weir, with the increasing of the upstream water head to the weir height ratio (
), the discharge coefficient decreases. The results showed that by increasing weir height, the discharge coefficient decreases for a given length of the weir. Linear weir and labyrinth weir without dentate create more water depth at the upstream by 3.3 and 1.2 fold compared with dentate labyrinth weir.
L. Babakhah, A. Khoshfetrat, E. Delavari,
Volume 29, Issue 1 (4-2025)
Abstract
Piano key weirs are a new form of labyrinth weirs and exhibit nonlinear characteristics. Due to their high efficiency regarding flow capacity, it is crucial to investigate local scour and identify solutions to mitigate it. Local scour was examined downstream of a trapezoidal piano key weir type B for the first time in this study. The weir was installed 5.50 m from the start of the channel and has a height of 0.20 m, featuring three cycles (three outlet keys, two inlet keys, and two inlet half keys). Three tailwater depths and three different flow rates were also utilized. The maximum scour depth increases with a higher densimetric Froude number and flow rate while decreasing with tailwater depth. The range of the dimensionless parameter for the densimetric Froude number in this study varies between 1 and 2. Additionally, sand and gravel were employed as two types of bed materials. As the diameter of the bed material increases, the maximum scour depth decreases. The scour index for gravel bed material is significantly lower than that for sand material, indicating that the risk of weir overturning is much lower in gravel bed material.
